In recent years, two communication technologies in particular have become commonly used by the general public: (1) mobile telephones; and (2) the Internet. Mobile telephones have provided users with the potential to always be reachable with reasonable service quality no matter where they are located. However, until recently, the primary service provided by mobile telephones has been speech. In contrast, the Internet has primarily provided data services. While flexibility for different services has been one of the Internet's strengths, the quality of services, such as, for example, Internet Telephony, has generally been unacceptable.
However, Internet Protocol (IP) Telephony has been gaining momentum thanks to recent technological advances. It is reasonable to predict that in the future, IP will become a commonly-used method of carrying telephony. Mobile telephony links could be based on IP telephony. In addition, mobile stations may also support not only audio and video, but also web browsing, e-mail, and gaming, for example. When IP telephony is employed, it is obvious that a fixed network at which wireless links terminate can be IP-based.
IP could be terminated at the interface between the fixed network and wireless links connected thereto; however, this would require special solutions to be implemented for each service supported over the wireless links. The flexibility of the services supported by the wireless links would therefore be limited. Thus, a solution implementing IP all the way from mobile station to mobile station over wireless links would have certain advantages.
Spectral efficiency is one of the main problems that must be overcome in order to implement IP from mobile station to mobile station over wireless links. It is of vital importance to use the scarce radio resources in a wireless network as efficiently as possible. One of the problems with use of IP over wireless links in the context of interactive voice conversations is large header overhead.
Speech data for IP telephony is most likely carried by the Real-time Transport Protocol (RTP). In RTP, a packet has, in addition to link layer framing, an IP version 4 header of 20 octets (i.e., 160 bits), a Universal Datagram Protocol (UDP) header of 8 octets, and an RTP header of 12 octets, resulting in a total header overhead of 40 octets. With IP version 6, the IP header is 40 octets, resulting in a total of 60 octets of total header overhead. The size of the payload depends upon speech coding and frame sizes used and may be as little as 15–20 octets.
The need to reduce header sizes for spectral-efficiency reasons is therefore apparent. Header compression is essential for providing spectrally-efficient voice over IP (VoIP) and multi-media services. Existing header compression schemes do not perform well over wireless links, primarily because of high error rates and long link round-trip times. Existing compression schemes include Compression RTP (CRTP), IP Header Compression (IPHC), and Point-to-Point Protocol Header Compression (PPPHC).
In an effort to develop an improved header compression scheme, the Internet Engineering Task Force (IETF) created the RObust Header Compression (ROHC) working group. ROHC provides a header compression framework that includes improved robustness, transparency, and spectral efficiency for wireless networks. A non-transparent solution, referred to as Good Enough Header COmpression (GEHCO), has also been proposed. GEHCO is intended to compress VoIP by removing all headers; however, GEHCO is unsuited for applications other than VoIP, such as, for example, multi-media and some related VoIP applications. Therefore, a general header compression framework, such as, for example, ROHC, that can accommodate a wide variety of applications that will exist in third generation wireless networks in a consistent yet customized fashion and under a unified framework is needed.
However, in order to provide needed highly-spectrally-efficient VoIP services on existing wireless network radio bearers, ROHC needs to be extended with a scheme that provides further compression beyond that which is currently possible via ROHC. It would be desirable to increase the compression possible under ROHC to the point that VoIP and other IP-based services could be implemented over wireless links with the same efficiency as voice services are currently implemented over the wireless links in a circuit-switched mode.
Referring now to the FIGURES, FIG. 3 is a block diagram that illustrates transmission of VoIP data packets in cdma2000. A system 300 includes a mobile station (MS) 302, a radio network (RN) 304, and a packet data service node (PDSN) 306. An arrow 308 representing a transmission path of data packets from the PDSN 306 to the MS 302 is also shown. Although not explicitly shown, it will be understood by those skilled in the art that a transmission path from the MS 302 to the PDSN 306 operates in a similar fashion to that described herein.
IP/UDP/RTP data packets 310 are shown in FIG. 3 entering the PDSN 306 at a network layer via the internet protocol (IP). As shown by the arrow 308, the data packets 310 pass through the link layer (e.g., PPP) and a radio-network-point-to-point protocol (R-P) interface before being transmitted over the RN 304. While in the RN 304, the data packets 310 pass through a Radio Link Protocol/Media Access Control (RLP/MAC) layer. From the RLP/MAC layer, the data packets 310 are received by the MS 302. At the MS 302, the data packets 310 pass through the RLP/MAC layer, the link layer (e.g., PPP), and the network layer (via IP), before emerging as UDP/RTP packets.
In cdma2000, all data traffic, including VoIP data packets, uses the point to point protocol (PPP) as the link layer. In cdma2000, there is a strong need to support VoIP and header compression on currently-existing radio bearers, rather than devising or optimizing new radio bearers for purposes of VoIP. One of the limitations imposed by many existing cdma2000 radio bearers is the capacity of the radio bearers to carry a compressed or uncompressed header.
There is accordingly a need for a method and system that permit compressed-header data packets to be sent over wireless links for applications such as, for example, VoIP, and that solve the above-mentioned and other problems associated with the prior art.